Light-sensitive photographic materials



United States Patent The present invention relates to a process for improving the quality of photographic materials and more particularly to a process for enhancing the developability and the general light-sensitivity of silver halide emulsion layers.

It is known that the general sensitivity of photographic silver halide emulsions can be increased by working up poly-glycols in the photographic material containing these emulsions (British patent specification 600,058).

It is also known that the same increase of sensitivity can be obtained by incorporating in the photographic material alkylene oxide polymers obtained by polymerizing alkylene oxide in the presence of dehydration products of heXitols, aliphatic alcohols, aliphatic acids, amines, amides and phenols (British patent specifications 592,676, 748,745 and 748,750).

It is further known that these polyglycols and alkylene oxide polymers should have a molecular weight of at least 400 and that in order to obtain a noticeable effect it is in practice necessary to use compounds which possess a molecular weight of 1500 to 2000 and more.

Contrary to the other known methods for increasing the sensitivity of silver halide emulsions, such as those wherein the chemical sensitizers increase the inherent sensitivity and those wherein the cyanine dyes increase the spectral absorption, it appears that the final sensitivity of the silver halide emulsion layers, wherein these compounds are incorporated, is higher, since these compounds exert a favorable influence on the development of these silver halide layers by means of appropriate developers. These compounds can thus be considered as development accelerators.

It is also known that these compounds, irrespective of the fact that they can be used for preparing emulsion layers with increased sensitivity, render these layers less suited for storage and specially for storage at high temperatures and high relative humidity, since these compounds cause a considerable increase of the fog.

It was further found that these compounds when added to a photographic element for obtaining a sensitive silver halide emulsion layer with increased sensitivity, impair the image tone and lead to brown and reddish-brown images.

It has now been found that the developability of lightsensitive emulsions can be very favorably influenced by adding to one or more emulsion layers or other layers comprised by the photographic element, compounds which are obtained by polymerizing or copolymerizing vinyl polymers bearing low molecular polyalkylene groups as side-chains and showing on themselves no action of development acceleration.

When applying this new method it was observed that on storage of these new compounds the image tone of the developed silver has remained unaltered.

These new compounds are vinyl polymers or vinyl copolymers bearing polyoxyalkylene groups as side-chains and consisting of recurring units of the following general R is a member selected from the group consisting of a hydrogen atom, a halogen atom, and an alkyl group;

R is a member selected from the group consisting of a carbonyl group and a NH-CO group;

R is an alkylene group selected from the group consisting of an ethylene group, a propylene group and an isopropylene group;

R is a member selected from the group consisting of a hydrogen atom, a hydrocarbon radical and a substituted hydrocarbon radical;

x represents a positive integer from 2 to 35, and

y represents a positive integer from 1 to 2 Monomer of methoxypolyethylene glycol-N-vinylcarbamate 10 g. of vinyl isocyanate, prepared according to the method described in the Belgian patent specification 540,975, are added to a solution of g. of methoxypolyethylene glycol (average molecular weight 550) in 50 cm. of anhydrous acetone. After the reaction, the acetone and any non-reacted vinyl isocyanate are distilled off under vacuum. 61.5 g. of the monomer of methoxypolyethylene glycol-N-vinylcarbamate are obtained.

PREPARATION 2 POLY- (METHOXYPOLYEIHYLENEGLYCOLN- VIN YLCARBAMATE) -CHz-CH L NHCO-(OCHg-GH2)mOC a |y 5 g. of the monomer according to Preparation 1 and mg. of aZo-isobutyronitrile are dissolved in 50 cm. of thiophene and anhydrous benzene. The solution is brought into a glass tube. After bubbling through nitrogen which is free of oxygen this tube is sealed and heated for 46 h. at 55 C. The content of the tube is poured into hexane and after drying of the obtained polymer a very viscous mass is obtained which is soluble in water.

The compounds according to the present invention may be added to the emulsions or brought into intimate contact with emulsion layers as follows: the compounds are dissolved in water or in an aqueous mixture of organic solvents which do not exert a prejudicial influence on silver halide emulsions. The obtained solution is then added to an emulsion or to an adjacent layer or applied to an emulsion layer as a coating composition.

The compounds can be introduced into the emulsion at various stages of its preparation, e.g., they may be incorporated as a separate addition, or mixed with one or more of the other constituents used at the initial precipitation of the silver halide grains during the physical or chemical ripening process, or at some other state prior to coating the emulsion.

The optimal amount of compound which can be added to the emulsion depends on the compound chosen, the nature of the colloid binding agent and the amount and kind of the silver halide in the emulsion. In general however the compounds according to the invention are added in a quantity of 50 mg. to 7 g. per mol of silver halide. If necessary, however, still other quantities of these compounds may be added which fall outside of these limits.

The process of the present invention can be combined with a method for increasing the sensitivity of the photographic material by incorporating therein small amounts of a sulphur containing compound such as allyl isocyanate, allyl thiourea and sodium thiosulphate, small amounts of reduction sensitizers such as the tin compounds described in the Belgian patent specifications 493,464 and 568,687, the imino-amino-methane sulphinic acid compounds described in the British patent specification 789,823 and small amounts of noble metal coni pounds such as gold, platinum, palladium, iridium, ruthenium and rhodium.

As a matter of fact the new process is advantageously superimposed on the sensitizing action of the compounds originally present in gelatin.

By application of the method according to the present invention stabilizers such as e.g. mercury compounds and the compounds described in our Belgian patent specifications 571,916 and 571,917 may be added to the emulsion. It is also usual to sensitize and to stabilize silver halide emulsions by incorporating therein cadium salts or by carrying out their processing in the presence of cadmium salts. Still other constituents such as antifogging agents, color couplers, developing substances, hardeners and wetting agents can moveover be added thereto in a usual manner and without deleteriously affecting the emulsion.

Thus they can be added with or without optically sensitizing dyestuffs. In the latter case this can occur before or after adding the dyestufis.

As a result of their property of conferring a better developability, the new compounds enhance the X-ray sensitivity and the general light-sensitivity of orthochromatic, panchromatic and all special emulsions, as well as of the ordinary non-spectrally sensitized emulsions. The new compounds may also be used with a variety of emulsions since the sensitivity is markedly increased in either negative or positive emulsions.

Hereinafter follows an example which illustrates our present invention without limiting, however, the scope thereof.

Example A washed coarsegrained gelatino-silver iodo-bromide negative emulsion (average grain size: 08 1,), wherein the silver halide consists of 94.5 mol percent of silver- ,4 bromide and 5.5 mol percent iodide, is ripened at 45 C. After adding a panchromatically sensitizing dye and other usual ingredients, the emulsion is coated on a suitable support (sample 1). Further samples are prepared by adding prior to coating, to the same emulsion and per mol of silver halide present, the amounts of developing accelerators listed below. They are then treated as sample 1. After drying and exposure they are developed for 7 min. at 20 C. in a solution of the following composition:

Water cm. 800 Monomethyl-p-aminophenolsulphate g 2 Hydroquinone g 5 Sodium sulphite (anhydrous) g Borax g 5 Potassium bromide g 0.5 Water to cm. 1000 SENSITOMETRIC RESULTS Sample Compound added Relative Speed Fog sensitivity None 100 0. 47 0.06 3.4 g. of methoxypoly-ethylene 104 0.49 0.10

gycol (average mol. weight 5 0 3 3.4 g. of methoxypoly-cthylene- 101 0.51 0.11

glycol (mol. weight 750). 4 3.4 g. of the polymer of prepa- 122 0.59 0.12

ration 2.

Although in the above example a gelatino-silver halide emulsion is used, our invention is not limited to such an emulsion. Emulsions containing other water-permeable colloids may equally well be treated according to the present invention. Among such colloids may be mentioned for instance: agar-agar; zein; collodion; watersoluble cellulose derivatives such as hydrolized cellulose acetate, cellulose-esters of hydroxy-carboxylic acids cg. lactic'acid and glycolic acid, and alkali metal salts of cellulose esters of dicarboxylic acids such as phthalic acid; polyvinyl alcohol; partially hydrolized polyvinylacetate; mono-esters of polyvinyl-alcohol and poly-basic organic acids such as e.g. maleic acid, described in the Belgian patent specification 568,153, interpolymers of vinylacetate with unsaturated compounds such as styrene and maleic acid, water-soluble polyvinyl acetals and other hydrophilic, synthetic, semi-synthetic and natural resins or polymeric compounds.

The new development accelerators may be used for sensitizing the known types of silver chloride-, silver bromide-, and silver iodide emulsions and also of emulsions containing mixtures of these silver halides.

The methods described above furthermore are not limited concerning the amount and the nature of the development accelerator to be added on the moment of the addition. For obtaining the optimum effect all particular techniques in the preparation of light-sensitive emulsions should be taken into account.

The new development accelerators according to this invention present the advantage of being compatible with color couplers and optical sensitizing dyes, which fact is of the greatest importance by using them for increasing the general light-sensitivity of color photographic material containing one or more light-sensitive layers.

A further advantage of the process according to the present invention results in the simplicity of its general application, such as e.g. in the manufacture of lightsensitive materials for amateur and professional photography and cinematography, for graphic processes and for scientific and industrial applications.

We claim:

1. Photographic light-sensitive element comprising a silver halide emulsion layer in intimate contact with a 5 6 polymer consisting of recurring units of the general foring a polymer consisting of recurring units of the genmula eral formula:

lCHPOH 1 0H,cH--- NHCO (OR2 )x0(C 2)n -J L wherein x represents a positive integer from 2 to 35, said polymer serving as a development accelerator for said silver halide emulsion.

wherein:

R is an ethylene group; n is an integer from 0 to 2, and x represents a positive integer from 2 to 35, said poly- 10 met serving as a development accelerator for said References Cited in the file of this Patent silver halide emulsion. 2. Photographic light-sensitive element comprising a UNITED STATES PATENTS silver halide emulsion layer, this emulsion layer contain- 2,467,832 Jones Apr. 19, 1949 

1. PHOTOGRAPHIC LIGHT-SENSITIVE ELEMENT COMPRISING A SILVER HALIDE EMULSION LAYER IN INTIMATE CONTACT WITH A POLYMER CONSISTING OF RECURRING UNITS OF THE GENERAL FORMULA 